Image sensor and method for power efficient readout of sub-picture

Abstract

An image sensor ( 1 ) comprising: an array ( 2 ) of pixels logically organized in rows and columns, the outputs of the pixels being connected to column lines (COLx) connectable to an array of buffers ( 3 ) via a routing block ( 10 ), the buffers being connected to an array of A/D convertors ( 4 ), the routing block ( 10 ) having a group of switches ( 6, 7 ) for reading sub-picture data, whereby the values of at least two rows of the sub-picture are distributed over the analog-to-digital-convertors before digitizing them in parallel. The entire sub-picture ( 21 ) may be digitized in one step. The routing block ( 10 ) may comprise an analog bus ( 9 ). The image sensor ( 1 ) further comprises a control circuit ( 8 ) for controlling the routing block ( 10 ) for routing pixel values on the column lines (COL) to a subset of the buffer array, the control circuit being adapted for supporting sub-pictures ( 21 ) with programmable positions and/or sizes.

The invention claimed is: 
     
       1. An image sensor comprising:
 a pixel array comprising a plurality of image pixels logically organized in rows and columns, the outputs of the pixels of each column of the pixel array being connected to a corresponding column line; 
 a buffer array comprising a plurality of buffers for each temporarily storing an analog value present on a column line; 
 an analog-to-digital convertor array comprising a plurality of analog-to-digital convertors operably connected to the buffers for converting the analog values stored in the buffers into digital values; 
 characterised in that 
 the pixel array comprises a sub-picture having a number of pixels larger than, or equal to, or less than the number of analog-to-digital convertors; 
 the image sensor further comprises a routing block connectable between the column lines and the buffer inputs, the routing block comprising a group of connection means for selectively operatively connecting at least one column line to at least two buffers; 
 the routing block being configurable in a full-resolution mode for routing each of the pixels of a selected row of the pixel-array to one of the buffers by interconnecting each of the column lines with its corresponding buffer; 
 the routing block being configurable in a sub-picture mode for routing the pixels of at least a first and a second row of the sub-picture to the buffers; 
 the image sensor being adapted for simultaneously digitizing the pixel values of the at least first and second row of the sub-picture by a single activation of the analog to digital converter array during the sub-picture mode; 
 a control circuit for controlling the routing block for routing the pixel values on the column lines to a subset of the buffer array. 
 
     
     
       2. The image sensor according to  claim 1 ,
 wherein the sub-picture has a number of pixels equal to, or less than the number of analog-to-digital convertors, and 
 wherein the routing block is configurable in a sub-picture mode for routing all the pixels of the sub-picture to the buffers; and 
 wherein the image sensor is adapted for simultaneously digitizing the pixel values of the entire sub-picture by a single activation of the analog to digital converter array. 
 
     
     
       3. The image sensor according to  claim 1 , wherein:
 the routing block further comprises an analog bus having a plurality of bus lines; 
 and wherein the group of connection means comprises a first subset of connection means for operatively connecting the column lines of the sub-picture to the analog bus lines of the analog bus, and at least a second and a third subset of connection means for operatively connecting the analog bus lines to the at least first and second subsets of the buffer array. 
 
     
     
       4. The image sensor according to  claim 3 , wherein the width of the sub-picture is an integer multiple of the number of analog bus lines. 
     
     
       5. The image sensor according to  claim 4 , wherein the width of the sub-picture is equal to the number of analog bus lines. 
     
     
       6. The image sensor according to  claim 1 , wherein the total number of pixels of the sub-picture is an integer multiple of the number of analogy-to-digital convertors or wherein the total number of pixels of the sub-picture is equal to the number of analog-to-digital convertors. 
     
     
       7. The image sensor according to  claim 1 , wherein the sub-picture is rectangular. 
     
     
       8. The image sensor according to  claim 1 , wherein the sub-picture has a programmable vertical position and/or a programmable horizontal position. 
     
     
       9. The image sensor according to  claim 1 , wherein the sub-picture has a predefined horizontal position or a predefined vertical position. 
     
     
       10. The image sensor according to  claim 1 , wherein the sub-picture has a vertical symmetry-axis, which is located substantially in the middle of the pixel array. 
     
     
       11. The image sensor according to  claim 1 , wherein the image sensor is a CMOS image sensor, and the group of connection means comprises NMOS transistors. 
     
     
       12. Method for reading the image data of a sub-picture of an image sensor according to  claim 1 , the method comprising:
 routing at least image data of the pixels of a first row of the sub-picture to a first subset of the buffers, and image data of the pixels of a second row of the sub-picture to a second subset of the buffers, and 
 thereafter, during the sub-picture mode, activating the analog-to-digital convertor array for performing simultaneous analog-to-digital conversion of the pixel values of the at least first and second rows of the sub-picture. 
 
     
     
       13. The method according to  claim 12 , wherein routing at least image data of pixels of a row of the sub-picture to the buffers includes routing the image data from a column to an analog bus line, and from the analog bus line to a buffer. 
     
     
       14. The method according to  claim 12 , wherein obtaining non-predefined location specifications about the sub-picture to be read includes receiving location specifications about the sub-picture from a processor having analysed an image on the array of pixels. 
     
     
       15. The method according to  claim 12 , wherein obtaining non-predefined location specifications about the sub-picture to be read includes receiving user defined location specifications about the sub-picture to be read. 
     
     
       16. The method according to  claim 15 , wherein receiving user defined location specifications comprises a user selecting the sub-picture to be read. 
     
     
       17. The method according to  claim 12 , wherein obtaining non-predefined location specifications about the sub-picture to be read comprises receiving information about position and/or size of the sub-picture. 
     
     
       18. The method according  claim 12 , wherein the sub-picture consists of a plurality of auto-focus pixels. 
     
     
       19. The method according to  claim 12 , further comprising: obtaining non-predefined location specifications about the sub-picture to be read, and wherein the routing of the image data is based on the obtained location specification.